Coating of glass and other objects with varnish film



March 12, 1935. c. w. BONNIKSEN 1,994,269

COATING OF GLASS AND OTHER OBJECTS WITH VARNISH FILM Filed Aug. 4, 195245 fects therein.

Patented. Mar. 12, 1935 UNITED STATES PATENT OFF ICE COATING F GLASS ANDOTHER OBJECTS WITH VARNISH FILM Cyril Wilfred Bonniksen, Slough,England, asv mot to Protectoglass Limited, London, Eng- ApplicationAugust 4, 1932, Serial No. 627,501 In Great Britain August 13, 1931 9Claims. (CI. 91-68) purpose which is in'view is the employment of glassso coated in connection withthe manufacture of so-called safety glass,that is to say glass combined with layers of a tough material, such ascelluloid, with the object of preventing I splinters from flying in theevent of fracture.

I According to the present lnventiona process for coating objects (forexample of glass) with a varnish-fllmconsists in applying a fllm.; ofvarnish dissolved in a solvent and thereafter treating the coated objectwith a treating-liquid which is capable of mixingv with the solvent butnot with the varnish.

The varnish may consist of a solution of a cellulose-ester (for examplecelluloid) dissolved in a solvent therefor (for example acetone). I

The invention comprises a process for coatin sheet material (for exampleglass) with celluloseester films characterized by feeding a film ofviscous liquid cellulose-ester varnish downwardly upon a surface of thesheet which is moving transversely relatively to the film and thereafterimmersing the sheet in a nearly horizontal positionin a bath of atreating-liquid which is capable of mixing with the solvent but not withthe varnish.

The treating liquid may be one which has a boiling point markedlydifferent from that of the solvent which it is to dissolve, and thesolvent be separated from the treating liquid after its treatment of thecoating by fractional evaporation, with or without re-use of thetreatingliquid and/or solvent cyclically.

One great advantage of treating the film in this way for the removal ofthe solvent is that evaporation of vthe solvent into the atmosphere isavoided, thereby obviating the use of expensive methods of collectingthe evaporated solvent. Another great advantage lies in the fact thatthere is no opportunity for specks o i dust out of the atmosphere tosettle upon the film and cause 'de- It has been found that thepresentinvention provides a means of obviating one of the defects which is mostcommon in films of thick or heavy varnishes and particularly varnishessuch as celluloid varnishes in which solvents such as .acetone areemployed. This defect consists in the development of bubbles in thevarnish film as it dries. It has been found that such bubbles;

are' due'to gases, particularly air; which become absorbed in theacetone or other solvent, and are released into the varnish-film as thesolvent evaporates and ceases to'be able to retain them' in solution.Both acetone and the treating liquid, such as castor oil, employedaccording to the present process readil'ydissolve air, but if containedgases, such as air, are removed from the treating liquid by subjectingit to a vacuum before use,pthe occurrence of bubbles is greatly reducedwhile if gases such as air are also removed from the varnish under avacuum the occurrence of bubbles may be entirely eliminated.

The occurrence of bubbles in thick celluloid varnish-films has hithertobeen inevitable upon drying, but it is found according to the presentinvention that it is possible to apply films of a thickness as great asfive thousandths of an inch .or more and to dry them without bubbles.

The following is a description by way of example of one form of theprocess according to the present invention with reference to theaccompanying drawing which shows diagrammatically part of an apparatusadapted to carry the invention into effect:-

In the drawing 11 represents a hopper having a feed slot 12 in thebottom thereof through which a film 13 of cellulose-ester solutioncontained in the hopper 11 may descend. The film 13 descends intocontact with a rotating roller 14 below the feed slot 12 except whenitmeets a transversely moving sheet of glass 15 propelled by rollers 16,17, in which case it becomes attached to the sheet and coated thereon.

The glass 15 which is fed beneath the feed slot 12 is glass which hasfirst been carefully cleaned and rendered entirely free of grease andall foreign substances so that the cellulose film will readily adhere toit. This may be efiected bypassing it through a washing machine such asis commonly employed for washing glass for photographic plates beforeapplying the sensitive emulsion thereto. The rate of feed of the glassby the rollers 16, 17 is arranged'to be very slight- .oil. The angle atwhich the sheets are caused to dip into the bath are such that thestill-liquid film of cellulose-ester solution will not run appreciablydown the face of the glass.

The roller 14 which receives excess cellulose film engages a doctor 20which scrapes off the excess and this is collected and made up againinto fresh solution for re-use. Covers 21, 22 are provided over theapparatus to keep out dust.

The solution in the hopper 11 may conveniently consist of celluloiddissolved in acetone. The strength of the solution will depend upon thetemperature at which it is fed from the slot, but good results have beenobtained by making a celluloid solution containing about 30% ofcelluloid and 70% acetone and cooling this to a temperature of- 8 C.before applying it to the glass. Cooling reduces evaporation of acetoneprior to passage into the castor oil bath 19.

In order to prevent the production of air bubbles on the fihn it isimportant that the celluloid solution in the hopper ll-should be airfree, and to this end it should be submitted to a vacuum in a treatmenttank prior to passage into the hopper 11. The obvious precautions offiltering the solution so as to render it free of contained specks anduniform in consistency need also, of course, to be observed.

The. castor oil flows through the bath 19 in a direction opposite to thedirection of passage of the glass sheets as shown by the arrows in thefigure and is withdrawn through outlets 23, 24. The temperature ofthebath is kept at about 35 C. and the length of the bath and the rate ofpassage of the glass through it is such that the glass is immersed inthe castor oil for about forty minutes. With a rate of travel of theglass of 15 inches per minute this corresponds to a length cyclically.This is secured by passing the outflow from the outlets 23, 24 to avacuum tank where it is subjected to reduced pressure. The reducedpressure serves to evaporate from the castor oil contained acetone aswell as to remove any air which it has absorbed and the air-free,solventfree castor oil is then returned to the bath 19.

After passage out of the bath 19 the glass is preferably passed into asecond and shorter bath of castor oil heated to a temperature of aboutC. for the purpose of extracting the final traces of acetone. Thereafterit'goes through a steam-heated oven where it attains a temperature ofbetween 80 and C. Finally the conveyor 18 takes the glass up to a seriesof rubber covered squeegee rollers which remove excess castor oil. Thecoating of the glass is then complete. It may be used for manufacturingsafety glass if desired as described in United States application No.627,502, filed August 4, 1932.

The thickness of the film applied to the glass may be very substantialwithout leading to the production of bubbles and apreferred thicknessfor the purpose of manufacturing safety glass is 0.008 of an inch.

' hol or even water. Petrol and water tend, however, to the productionof bubbles in the film, and alcohol tends to leave a flabby coating.

Castor oil is a solvent for camphor as well as for acetone and it isfound that camphor in the celluloid is extracted with the castor oil inaddition to its extraction of acetone. Consequently a 1. A process forcoating sheet material with a cellulose-ester film consisting inpreparing a solution of cellulose-ester in a solvent therefor, removingair from the solution by sub ecting it to a vacuum, feeding a film ofsaid sol ion downwardly upon a surface of the sheet material whilemoving the sheet transversely relatively to'the film, thereafterimmersing the sheet in a bath of a vegetable oil which has been freed ofair under vacuum so as to dissolve solvent from the cellulose-ester filmwithout producing bubbles therein and finally removing the vegetableoil.

2. A process for coating glass sheets with a cellulose-ester filmconsisting in preparing a solution of cellulose-ester in a solventtherefor, re-

moving airfrom the solution by subjecting it to a vacuum, feeding a filmof said solution downwardly upon'a surface of the glass while moving thesheet transversely relatively to the film, thereafter immersing thesheet in a bath of a vegetable oil which has been freed of air undervacuum so as to dissolve solvent from the cellulose-ester film withoutproducing bubbles therein and finally removing the vegetable oil.

3. A process for coating sheet material as claimed in claim 1, whereinthe solvent employed for the cellulose-ester is one having a, boilingpoint markedly different from that of the vegetable oil and is separatedfrom the vegetable oil after application of the latter to the sheetmaterial by fractional evaporation.

' 4. A process for coating glass asclaimed in claim 2, wherein thesolvent employed for the cellulose-ester is one having a boilingpointmarkedly different from that of the vegetable oil and is separatedfrom the vegetable oil after application of the latter to the glass byfractional evaporation.

5. A process for coating sheet material with cellulose-ester filmscharacterized by feeding a film of viscous liquid cellulose-estervarnish downwardly upon a surface of the sheet which is movingtransversely relatively to the film and thereafter immersing the sheetin a nearly horizontal position in a bath of a treating-liquid which iscapable of mixing with the solvent but not with the varnish andsubjecting the treating liquid to a vacuum to remove contained ,gases,before immersing the sheet therein.

6. A process for coating glass sheets with cellulose-ester films,characterized by feeding a film of viscous liquid cellulose-estervarnish downwardly upon a surface of the glass sheet while moving saidsheet transversely relatively to thefilmsoastocoatthesheetwiththefilmand thereafter immersing the sheet in anearly horizontal position in a bath. of a treating liquid which iscapable of mixing with the solvent but not with the varnish andsubjecting the treating liquid to a vacuum to remove contained gases,before immersing the sheet therein.

7. A process for coating objects with a varnish film consisting oftaking varnish dissolved in a solvent, eliminating air therefrom bysubjecting it to a vacuum, thereafter coating the object with thevarnish, and finally treating the varnish with a treating liquid capableof mixing with the solvent but not with the varnish, so as to remove thesolvent therefrom, the said treating liquid having the contained gases,such as air, removed therefrom by subjecting it to a vacuum before use.

8. A process for coating glass with a varnish film consisting of takingvarnish dissolved in a solvent, eliminating air therefrom by subjectingit to a vacuum, thereafter coating the glass with the varnish, andfinally treating the varnish with a treating liquid capable of mixingwith the solvent but not with the varnish so as to remove the solventtherefrom, the said treating liquid having the contained gases, such asair, removed therefrom by subjecting it to a vacuum before use.

9. A process for coating objects with a cellulose-ester varnishconsisting in first subjecting a solution of a cellulose-ester in asolvent therefor to a vaccum to eliminate air, thereafter applying theair-freed solution to the object, and finally removing the solvent bytreating with a liquid capable of mixing with the solvent but not withthe cellulose-ester, said liquid having the contained gases, such asair, removed from it by subjecting it to a vacuum before use.

CYRIL WILFREH) BONNIKSEN.

